In rotating turbomachinery such as compressors, impeller wheels are mounted to a rotating shaft, which is driven at high rotational speed. The rotating shaft may be coupled to the shaft of motor or a turbine, deriving power therefrom. In some applications, a common integrated compressor/motor shaft may be used. During rotation of impellers under high load at a high rotational speed, thrust force generated by a high centrifugal force as well as a pressure differential appearing across each of the impellers is exerted on the impellers. To prevent an occurrence of slippage of the impellers on the shaft under the effect of this thrust force, there has been employed a method of fixedly mounting impellers on the main shaft by shrink-fitting instead of the conventional methods using spline keys, press fitting or the like means.
Conventionally, shrink-fitting of impellers on to the shaft is achieved by heating the impeller uniformly to a high temperature, causing the hole/opening of the impeller to radially expand. For example, the impeller is heat soaked in an oven to a temperature of about 257° F. (125° C.). The impeller is then removed from the oven and the shaft is inserted into the impeller hole. Upon cooling, the mass around the hole shrinks back to its original size and frictional forces create a highly secure fit.
However, shrink-fitting using heat provides limited flexibility in the assembly of the rotating machine since is only possible when the shaft is free and not already built in to the rest of the components of the rotating machine.
The document NL-A-6806392 discloses a method for hydraulically mounting a hub, such as a propeller, on to a conical portion of a shaft by pressured hydraulic fluid acting in radial and axial directions on the hub. However the arrangement as disclosed in the document is not suitable for hydraulically mounting multiple hubs on to the same shaft.